FIG. 34 is a schematic view of a conventional irregular pattern reader, as is described in, for example, the Japanese Patent Publication (unexamined) Sho. 550 12442. In the drawing, reference symbol L is an incident luminous flux from a light source 100. Reference numeral 101 a fingerprint detection prism. Numeral 102 is an incident plane of the detection prism 101, which is a plane on which the incident luminous flux L is incident. Numeral 103 is a detection surface of the detection prism 101, and is a base on which a finger is put to detect a fingerprint. Numeral 104 is an emission plane, which is a plane from which light reflected from the detection surface 103 is emitted. In the detection surface 103 of the detection prism 101, an incident angle (θI) of the incident luminous flux is not less than a critical angle (θc) to the air.
Numeral 105 is a person's fingertip having an irregular pattern as a subject to be detected. Numeral 106 is an irregular pattern of a fingerprint or the like. Numeral 107 is an image pick-up device for picking up an image of the irregular pattern 106 of the fingerprint, being light reflected from the detection surface 103. Numeral 108 is a processor for processing the image picked up by the image pick-up device 107. Numeral 109 is an image-forming lens for forming the image of the fingerprint pattern onto a light-receiving plane of the image pick-up device 107. The image pick-up device 107 is, for example, a television camera.
Described below is operation of the conventional irregular pattern reader of above construction. When the incident luminous flux L incoming from the incident plane 102 irradiates the fingertip 105 on the detection surface 103 of the detection prism 101, since the incident angle (θI) of the incident luminous flux L is not less than the critical angle (θc) to the air and not more than a critical angle to a finger, light is transmitted to the finger at a portion where a projection face of the fingerprint or the like is in close contact with the detection surface 103, and less light is reflected from the detection surface 103. On the other hand, when there is an air layer due to a recession face of the fingerprint or the like between the detection surface 103 and the fingertip 105, the incident light is totally reflected on the detection surface 103. An image reflected on the detection surface 103 is detected by the television camera as the image pick-up device 107 and is processed by the processor 108, and thus pattern information of the fingerprint is obtained.
Since the conventional irregular pattern reader shown in FIG. 34 is constructed as described above, in order to pick up an image with less distortion, it is necessary that the image-forming lens be sufficiently distant from the fingerprint detection surface. Therefore, the whole length of the reader becomes long, and an optical path from the light source to the fingerprint detection prism and an optical path from the detection surface of the fingerprint detection prism to the image-forming lens cross each other at right angles. As a result, a problem exists in that the reader becomes thick and large.
The present invention was made to solve the above-discussed problems, and has an object of providing a small and thin irregular pattern reader.